Mundra Thermal Power Plant, Mundra, Gujarat, India

The nine-unit Mundra thermal power plant is one of the largest coal-fired plants in the world, but it takes up minimal space and uses both fuel and water efficiently.

PWR_1014_TP_Mundra_Splash

In the October 2013 issue of POWER, Tata Power’s 4-GW Mundra ultra-mega power plant was recognized with a Top Plant award in the coal category. This year POWER recognizes another behemoth in the region—and not only for its scale.

India’s Power Sector

As of June 30, 2014, India’s installed power capacity was roughly 249.5 GW. As much as 59.51% of this total—about 148.5 GW—was coal-based thermal power.

Based in Ahmedabad, in the state of Gujarat, Adani Power added 2,640 MW, or 15.5% of India’s total power capacity additions of about 17,000 MW, in the 2013–14 fiscal year. Every addition of electrical power is crucial in a country where roughly one-quarter of its more than 1.2 billion people have no access to electricity, according to the World Bank.

Adani Power operates coal-fired power plants at three locations: the 3,300-MW Tiroda plant, the 1,320-MW Kawai plant, and the 4,620-MW Mundra Thermal Power Plant (TPP). Three more are in development: Chhindwara (1,320 MW), Dahej (2,640 MW), and Bhadreshwar (3,300 MW).

But the Mundra TPP, developed to provide power for the Adani Ports and Special Economic Zone in Mundra, is the company’s flagship. Built at a cost of $4.6 billion ($3.7 billion of it debt and $939 million equity), its four 330-MW subcritical units and five 660-MW supercritical units produce a staggering 4,620 MW, making it the world’s largest single-location private sector thermal power station. The plant has an 85% load factor (the national average is 74%).

Adani Power CEO Vneet Jaain explained that all generation is supplied through power purchase agreements: 46% to the state grid and 54% to the national grid.

Design and Development

“Our Mundra plant sets global benchmarks for power producers in terms of size, efficiency and sustainability,” said Jaain. “Despite its enormous capacity, the facility stands unique in the world when compared with area per megawatt, located as it is on a very optimized layout of 734 acres, alongside auxiliaries like cooling towers, a 47-mld [million liters a day] desalination plant and the flue gas desulfurization [FGD] plant.” India’s Central Electricity Authority allows for 0.5 acre per megawatt, which for the Mundra TPP could have meant 2,310 acres—over three times its actual area.

The plant was readied in record time for any Indian power developer. Groundbreaking was in December 2006, and there were just 34 months between synchronization to the grid of the 330-MW Unit 1 on May 23, 2009, and of the 660-MW Unit 9 on March 5, 2012.

The plant was also the first to introduce the 660-MW supercritical power technology into India, with the commissioning of Unit 5 in December 2010, following installation of the four 330-MW units. The 330-MW Unit 1 was the first such subcritical boiler at a power plant in India. The 660-MW boilers were supplied by Harbin Boiler Co. and the turbine generators by Dongfang Machinery Co.; the 330-MW boilers were provided by Babcock & Wilcox Beijing Co. Ltd. and the turbine generators by Beijing Beizhong Steam Generator.

The supercritical boiler is of a once-through type, unlike the subcritical boiler, where water and steam remain in saturated condition in the boiler drum and water is recirculated for generation of steam. The 600-MW supercritical turbine has three cylinders, including a combined high-pressure and intermediate pressure section, and is configured as tandem compound with four-flow exhaust to the condenser.

“As supercritical power plants operate at higher temperature and pressure, they achieve higher efficiencies (above 40%) than conventional subcritical power plants (32%),” said Singh. “The use of supercritical technology also leads to significant CO2 emission reductions, of above 20%.”

Transmission Constraints

On Dec. 31, 2013, the plant set an Indian power sector record by surpassing its 4,620-MW nameplate capacity to generate 4,644 MW. To enable that record and to circumvent the government’s infirm transmission network, Adani Power had two power lines constructed: the 433-kilometer (km) 400-kV transmission line to transmit 1,000 MW from Mundra to Dehgam in Gujarat and the 989-km 500-kV high-voltage direct current (HVDC) bipole line with the capacity to transmit 2,500 MW from Mundra to Mohindergarh in the northern state of Haryana. The latter is the first HVDC system in the private sector in India.

While Siemens India was contracted to build the HVDC substations at Mundra and Mohindergarh, the HVDC line was constructed by Jyoti Structures Ltd., both works taking three years till commissioning in July 2012. The Mundra-Dehgam line was constructed in sections by Jyoti and Kalpataru Power Transmission Ltd., taking two years till commissioning in July 2009.

Coal Supply

The Mundra TPP is a significant milestone in the path to realizing Adani Power’s target of generating 20,000 MW by 2020. By that year, the Adani Group is also seeking to mine 200 million metric tons (mt) of coal and handle 200 million mt of cargo from its ports.

At full load, the plant consumes about 55,000 mt of coal per day, though its yearly consumption is between 16 and 17 million mt. It runs on blended subbituminous coal, about 70% imported from the Adani coal mine in Bunyu, in Indonesia’s East Kalimantan province, and the rest from the public sector Mahanadi Coalfields in the eastern Indian state of Odisha. The coal is freighted to the Adani Group’s Mundra port, India’s largest, which notched a throughput of 100 million mt in 2013–14 and which is slated to become the largest coal import terminal in the world. From there, a high-speed conveyor belt conveys the coal to the plant 9.5 km away at 6,000 mt per hour.

The Mundra TPP, named after the coastal town near which it is located in the arid Kutch district, operates in far-from-conducive conditions. “We are constantly challenged by a highly corrosive and saline ambient condition, with average wind speeds between 20 and 40 kmph that affect the performance of the cooling towers,” said Station Head Anand Kumar Singh. “Besides, our plant has been designed to operate with high, 33% moisture coal.” High-moisture coal can choke coal-handling chutes and coal feeders, reduce mill output, and increase the heat rate, he explained. To reduce the moisture content, the coal is pulverized to coal fines that are then admixed in a drying chamber with a dry gaseous mixture.

Maximizing Seawater Usage

Mundra is India’s largest TPP to function on a seawater-based closed-cycle induced draft circulating cooling water system. The system draws on seawater that is recycled up to four times, conserving water and requiring a smaller discharge pipeline into the sea than an open-circuit cooling system.

Though seawater is used for the cooling system, other auxiliary systems use seawater purified by a reverse osmosis plant that can produce 47 million liters of freshwater every day.

Boilers require demineralized water that is produced in demineralization plants. Each 660-MW boiler can convert more than 2,000 mt of water per hour into steam that is 250 times the atmospheric pressure and at a high of 570C. Steam is sent to the turbine through high-pressure pipes, after which it is collected and indirectly cooled in a condenser with seawater and recycled back to the boiler.

Jaain said plant equipment is protected against high corrosiveness and salinity by using the right type of coatings, sacrificial anodes, and impressed current cathodic protections. “There is a three-year rolling schedule for structural painting, a changeover schedule for equipment that handles seawater, and anti-corrosive coatings for reinforced cement concrete structures,” he added. At times, windborne drifts from the cooling towers cause salt deposition on the switchyard insulators, which leads to tracking on the high-kV insulators, resulting in unit trips. To counter this, a special protective coating is applied to the insulators at fixed intervals.

Environmental Controls

The FGD system, supplied by Alstom India, requires only seawater as the adsorbent (no alkaline chemicals) to reduce sulfur emissions (Figure 1). Its simplified structure—comprising an adsorption tower, seawater supply pump, and aerator—renders operation and maintenance (O&M) easy, said Associate General Manager (O&M) Girish Raghuwanshi. “No by-products are formed, and the adsorbents can be released into the sea after adjusting their pH, chemical oxygen demand, and dissolved oxygen,” he explained. “Increase of sulfate in the seawater returned to sea is within natural seawater variations, and emissions too are well within the norms prescribed by the Gujarat Pollution Control Board, which are 50 mg/Nm3 for particulate matter, 100 ppm of SO2, and 50 ppm for nitrogen oxides.”

PWR_1014_TP_Mundra_Fig1
1. Seawater system. At the Mundra plant, only seawater is needed by the flue gas desulfurization system to reduce sulfur emissions to required levels. The nine units share four stacks, Units 1 and 2, 3 and 4, and 5 and 6 having three separate stacks with two flues each, while Units 7, 8, and 9 have one stack with three flues. Courtesy: Adani Power Ltd.

The Mundra TPP is researching the expanded usage of the fly ash it generates, as a liming material and as a feedstock for vermicomposting (converting organic waste into fertilizer). Most of the fly ash is conveyed to three 3,000-m3 silos. From there, trucks dispatch it to makers of bricks, ceramics, cement and roads; it also is packed in 1.4-mt bags for shipment to the Middle East.

In the first experiment of its kind in India, 23 mt of vermicompost have been produced to date and provided to surrounding villages, said Adani Power COO Jayadeb Nanda. Its production involves mixing equal portions of fly ash and organic matter, in the form of cow dung, and incubating this mixture with anecic earthworms for 50 days. This spawns phosphate-solubilizing bacteria that convert the insoluble minerals from fly ash into more soluble forms, enhancing the bioavailability of the nutrients in the vermicomposted series. Nanda says cattle dung is available in abundance from villages near the project, facilitating the management and disposal of agricultural as well as industrial wastes.

Wider Impact

The Mundra TPP is visited by power professionals and engineering students from India and beyond for refresher courses and training provided by its state-of-the-art Training & Research Institute.

“With success comes responsibility, so we take care to reinvest in protecting and developing the communities within which we live and operate,” said Gautam Adani, whose wife Priti heads the Adani Foundation, the Group’s corporate social responsibility arm. “We invest 3% of our group profit in community initiatives through the Adani Foundation.” In Mundra, these include a 50-bed hospital, mobile health care, rural dispensaries, two large and several small play schools, provision of drinking water, watershed management, counseling and assistance in advanced farming techniques, groundwater conservation, and skill-building for traditional artisans. ■

Sarosh Bana is executive editor of Business India.